The objective of the proposed work is to define the role which functional sympathetic innervation plays in the development of heart metabolic and functional characteristics. Full functional sympathetic innervation has been implicated in the control of cell differentiation in the developing heart as well as in the control of myocardial contractile protein properties in the adult heart. Developmentally related alterations in the heart include enhanced aerobic metabolic capacity, enhanced contractile protein enzymatic (ATPase) properties, and enhanced contractile performance. The above developmentally related cellular and subcellular alterations occur in a time sequence which is closely related to the development of full functional sympathetic innervation in the heart and sympathetic neural activity has been shown to influence other heart developmental aspects. Therefore, it seems likely that the level of sympathetic neural activity may represent a single, underlying mechanism which coordinates perinatal cardiac muscle development. Physiological and biochemical measurements will be utilized to correlate the development of heart contractile function with myocardial metabolism and contractile protein characteristics. The relationship between development and development in the presence of both enhanced and reduced sympathetic neural activity will be determined. This information will establish the potential cardiac cellular and subcellular lesions which may be assocciated with abnormal cardiac innervation in infants and neonates. If alterations in cardiac sympathetic nervous system activity can be shown to result in abonormal cellular characteristics, then a neurally mediated, cellular basis for heart dysfunction associated with sudden infant death syndrome (SIDS) may be identified.